The objectives of this proposal are to examine the taste responsiveness of peripheral gustatory neurons of the hamster that have not been previously characterized, to determine the nature of the gustatory information transmitted to the brainstem by the various taste bud populations, and to examine the roles played by these various receptor inputs in the control of taste-elicited orofacial reflexes. Responses of single taste fibers in the glossopharyngeal (IXth) nerve and in the pharyngeal and superior laryngeal branches of the vagus (Xth) nerve will be recorded electrophysiologically to a wide array of chemical stimuli applied to the taste bud populations innervated by these nerves. These responses will be examined with multivariate statistical procedures in an attempt to categorize the fibers in these peripheral nerves on the basis of similarities in their response profiles. The patterns of orofacial responses elicited by this same array of chemical stimuli will be examined in normal hamsters using high-resolution videotape recording and frame by frame analysis. The contribution of the various taste bud populations (in the fungiform papillae, nasoincisor ducts and soft palate, circumvallate and foliate papillae, and nasopharyngeal and epiglottal regions) to the expression of these orofacial responses will be examined in animals with partial denervations of the gustatory afferent nerves, including the chorda tympani, greater superficial petrosal, glossopharyngeal, and pharyngeal branch of the vagus nerve, singly and in combination. Finally, responses of single neurons in the nucleus tractus solitarius will be recorded electrophysiologically as the various taste bud populations are stimulated separately. The isolation of a given taste bud region will be insured by recording from animals in which all other taste inputs to the medulla have been acutely transected. The anatomical organization of these cells will be reconstructed with respect to their afferent nerve supply and their gustatory sensitivities. This series of experiments is designed to provide a greater understanding of the normal organization of the mammalian gustatory system than is now available, addressing the roles of the various taste bud populations in taste-mediated orofacial reflexes. Greater knowledge of the normal neurophysiology and anatomy of the gustatory system can provide a basis for assessing the involvement of the several taste bud populations in various disease states, particularly those involving craniofacial pathology.